Description of Horse

﻿Horses and zebras, members of the Equidae family, share common anatomical traits such as hard hooves, strong spinal columns, muscular arching necks, sloping shoulders, wide hindquarters, high-crowned teeth, slender legs, and elongated heads. Size and coloration varies according to specific horse breeds developed through selective breeding. Similar differences in zebra species have evolved due to natural selection and environment. Horses and zebras are related to wild asses and donkeys and represent five species of the genus Equus.

Anatomy Development

Eohippus was the ancestor of both domestic and wild horse species.Aleaf-eatingmammalas small as a fox, Eohippus lived during the Eocene epoch and had several toes on its feet. Descendants gradually grew larger, lost toes, and became grass grazers. Przewalski's horse, indigenous to Mongolia but not seen in the wild since 1968, links ancient and modern horses. Because it has sixtysix chromosomes and domestic horses have sixtyfour, Przewalski's horse is a separate wild horse species and not an ancestor of modern horses. A hybrid produced by a horse and a Przewalski has sixty-five chromosomes and is fertile. Modern horses and zebras are distinguished by a single hoof on each foot. Vestigial remains of prehistoric toes are located above hooves. Horses and zebras have long skulls and jaws that hold approximately forty to forty-four permanent teeth, including incisors to bite grass and molars to chew roughage. The teeth have long crowns that slope with age and can be examined to determine how old an animal is. Horses use their teeth to eat, groom, and fight. The horse's digestive system is bigger and more efficient than that of carnivores, and has approximately 40 meters (131 feet) of intestines with a meter-long cecum attached to the colon. Horses and zebras live on grasslands ranging between sea level and mountains and eat mostly fibrous food such as hay, grain, and oats. Food ferments in the cecum, which can hold as much as thirty-eight liters (ten gallons). Horses eat an average of sixteen hours per day to sustain their systems. The average horse's heart weighs about 3 kilograms (6.6 pounds), and the surface area of a horse's lungs measures approximately 2,500 square meters (8,200 square feet). Horses' weight varies from minimums of nearly 500 kilograms (1,000 pounds) to maximums of more than 908 kilograms (1 ton). Fifty-one vertebrae are in horses' spines from the top of the skull to the base of the tail. Horses' eyes are placed on the sides of their heads, enabling them to see the horizon without moving their head. Their eyesight is better than that of dogs. Horses depend on hearing more than sight, but rely most on the sense of smell. The flehmen response is when the horse raises its upper lip to indicate it has smelled something interesting.